Chapter 6
Common Units of Measure: Storage, Throughput, and Speed
Information technology is always seeking to transmit, receive, store, and locate information as quickly as possible. With the rise of cloud computing, digital photography, and HD video, the need for storage has never been greater. Understanding the units of measure used for storage, throughput, and processing speed is essential in any IT field. This chapter covers CompTIA IT Fundamentals+ Objective 1.5: Compare and contrast common units of measure: storage units (bit, byte, KB, MB, GB, TB, PB), throughput (bps, Kbps, Mbps, Gbps, and Tbps), and processing speed (MHz, GHz).
Foundation Topics
Storage Units
Storage units measure the capacity of permanent storage, including magnetic, optical, and flash memory drives; read-only memory (ROM) and random-access memory (RAM, a.k.a. temporary storage). Storage units use two number systems: decimal powers of two and decimal powers of ten. Therefore, it’s important to note which numbering system is being used for a particular device’s storage capacity.
Bit
The smallest storage unit is the bit. A bit is the 0 or 1 in binary (base 2) numbering. A nibble is equal to four bits.
Note
See Chapter 2, “How Computers Store Data: Notational Systems,” for more about binary numbering.
Bits
The term bits (plural) refers to the size of the internal registers in a CPU (processor). A 32-bit processor can process information in 32-bit-wide elements and can also access memory addresses up to 232 (4,294,967,296 or 4GB). A 64-bit processor can process information in 64-bit-wide elements and can also access memory addresses up to 264 (18,446,744,073,709,600,000, or 18 ZB [zettabytes]).
Note
Make sure you understand the differences between 8-bit, 16-bit, 32-bit, and 64-bit numbers versus RAM and application requirements. The differences between 32-bit and 64-bit operating systems and their memory limits are critical to exam success. For example, if a 64-bit processor uses a 32-bit operating system, the maximum amount of RAM (maximum number of memory addresses) the processor can address is the 32-bit limit (4GB).
Byte
A byte is equal to eight bits. A single character in a plaintext file requires a byte to store it. Multiples of a byte are used by all larger units of measure.
KB
Depending on the device, a kilobyte (KB) is either 1024 bytes (decimal, power of two) or 1000 bytes (decimal, power of ten).
Note
KB, MB, GB, and larger measurements based on powers of two are sometimes referred to as binary measurements, although they use decimal numbering.
MB
Depending on the device, a megabyte (MB) is either 1,048,576 bytes (1024 kilobytes using powers of two) or 1,000,000 (one million) bytes (decimal, powers of ten). Typically, RAM (system memory or cache memory) is expressed using the powers-of-two method, whereas the rated capacity of storage drives and media is expressed using decimal measurements.
To calculate the binary MB value from a value in millions, divide the capacity in bytes by 1,048,576. In Figure 6-1, the operating system (Windows 10) displays both values using the properties sheet for a partially used CD-R disc. The space used on this CD-R disc is over 166 million bytes, which converts to 158MB using binary (powers of two) MB.
Note
Some current hard disk drives have a 64MB disk cache. The disk cache is RAM built in to the drive to improve read/write performance. A 64MB disk cache has a capacity of 67,108,864 bytes (64 binary MB).
GB
Depending on the device, a gigabyte (GB) is either 1,073,741,824 (1024 megabytes in powers of two) or 1,000,000,000 bytes (decimal, powers of ten). To add to the potential for confusion, device manufacturers and operating system vendors use both methods to describe capacity.
For example, a typical 32GB flash memory card or USB drive has a capacity of 31,880,904,704 bytes (nearly 32 billion bytes), as measured by the manufacturer. However, Windows uses both decimal bytes and binary GB to express drive capacity, so the same drive has a capacity of 29.6GB using the binary (powers of two) measurement system.
However, 32GB of RAM (which could be installed as 4×8GB or 2×16GB memory modules) provides a workspace of 34,359,738,368 bytes, because memory is measured using binary GB.
To calculate the binary GB value from a value in billions, divide the capacity in bytes by 1,073,741,824. Figure 6-2 illustrates how Windows displays the capacity of a single-sided DVD+R disc. This disc is described by the vendor as a 4.7GB disc.
TB
A terabyte (TB) is either 1,099,511,627,776 bytes (1024 gigabytes using powers of two) or 1,000,000,000,000 bytes (powers of ten). Storage vendors generally measure their drives using powers-of-ten capacities, whereas operating systems use powers-of-two capacity (binary) measurements. See Figure 6-3 for an example of the capacities of two multi-TB drives.
PB
Depending on the device, a petabyte (PB) is either 1,125,899,906,842,620 (1024 terabytes using powers of two) or 1,000,000,000,000,000 bytes (decimal, powers of ten). Petabyte-sized drive arrays are used in cloud storage and backup systems.
Capacity Comparison
Table 6-1 compares the capacity of binary KB through PB.
Table 6-1 Binary KB–PB Capacity in Bytes
Measurement |
Name |
Size (Bytes) |
1KB |
Kilobyte |
1,024 |
1MB |
Megabyte |
1,048,576 |
1GB |
Gigabyte |
1,073,741,824 |
1TB |
Terabyte |
1,099,511,627,776 |
1PB |
Petabyte |
1,125,899,906,842,620 |
Ever wonder how much space a digital photo takes? A 3-minute MP3 song track? A one-page Microsoft Word file? Table 6-2 compares typical space requirements for common data file types.
Table 6-2 Common Data File Types and Typical Sizes
File Type |
Details |
Size (Bytes) |
Size (Binary KB/MB) |
Notes |
JPG |
Digital photo taken with smartphone |
2,981,608 |
2.84MB |
5312×2988 resolution* |
CR2 |
RAW (uncompressed) image file taken with Canon digital SLR (DSLR) camera |
29,593,050 |
28.2MB |
5184×3456 resolution* |
XLS |
Microsoft Excel file (single worksheet), with 500 rows and 12 columns |
89,777 |
86.6KB |
|
DOCX |
Microsoft Word file (one page, text with styles) |
30,578 |
28.8KB |
|
DOCX |
Microsoft Word file (five pages, including two charts and one color photo optimized for printing) |
2,246,151 |
2.14MB |
|
Five-page Adobe Reader file containing text, two charts, and one color photo optimized for printing converted from a DOCX file |
448,102 |
437KB |
|
|
MP3 |
Digital music file |
13,785,280 |
13.1MB |
|
MP3 |
Digital music file |
21,161,54 |
20.1MB |
|
MP3 |
Digital music file |
3,079,105 |
2.93MB |
* number of pixels (horizontal×vertical) in still image
** Duration (minutes:seconds)
^ Quality (compression setting, where lower quality = smaller file size)
Throughput Unit
Throughput units are used to measure the speed at which data is transferred between endpoints, such as from the Internet to a broadband modem, or from a hard drive to a computer. Throughput units use powers-of-ten (decimal) numbering systems.
bps
Bits per second; divide by 10 to determine Bps (bytes per second). Used mainly to measure the speed of early dial-up (analog) modems.
Kbps
One kilobit per second equals 1000bps. Currently, Kbps is primarily used to measure the speeds of low-performance DSL Internet connections (256–768Kbps). Figure 6-4 compares the speeds of early Internet access devices.
Mbps
One megabit per second equals 1000Kbps. Mbps is widely used to measure the speeds of high-speed and broadband Internet connections, LAN connections, and I/O devices such as USB 1.1, USB 2.0, and FireWire. Figure 6-5 compares the speed of these connections.
Gbps
One gigabit per second equals 1000Mbps. Gbps measurements are primarily used to express the speeds of very fast Internet and LAN connections (Gigabit Ethernet and 10G Ethernet, for example), and the speed of high-performance device interconnects, such as USB 3.1 Gen 1 (5Gbps), USB 3.1 Gen 2 (10Gbps), and SATA Revision 3 (6Gbps). Figure 6-6 compares these devices.
Tbps
One terabyte per second equals 1000Gbps. Tbps is used mainly to measure the speeds of Internet connections between countries and regions.
Note
If you need to convert a measurement such as Mbps (megabits per second) to MBps (megabytes per second), divide the measurement by 10. For example, 480Mbps (USB 2.0 transfer rate) is the same as 4.8MBps.
Processing Speed
Processing speed (also known as clock speed) measures the number of cycles a processor can perform per second. The processing speed is controlled by a crystal oscillator clock chip on the motherboard. Each combination of a pulse and rest is a clock cycle (see Figure 6-7).
Note
To learn more about motherboards and other components found inside a computer, see Chapter 10, “Explain the Purpose of Common Internal Computer Components.”
When processors with the same internal design but different clock speeds are compared, the processor with the faster clock speed can perform more work in a given amount of time.
Note
Processors not only vary in their clock speed but in other design factors such as the number of operations that can be performed during a clock cycle and the presence and size of memory caches (which reduce the need to check main memory for the next operation to perform). For these and similar reasons, comparing processors that use different internal designs by clock speed will lead to incorrect conclusions about performance.
MHz
One megahertz (MHz) equals 1 million cycles per second. The original IBM PC (1981) had an Intel 8088 processor running at 4.77MHz (4,770,000 cycles per second). By 1986, the Intel 80286 processor ran at 12MHz (12,000,000 cycles per second). By 1999, Intel and AMD processors were running at clock speeds exceeding 500MHz (500,000,000 cycles per second).
Note
MHz is also used to measure the I/O bus clock rate used by memory modules. To determine the data rate (transfer rate) of common memory modules (DDR, DDR2, DDR3, and DDR4), multiply the memory clock rate by 2.
GHz
One gigahertz (GHz) equals 1 billion (1,000,000,000) cycles per second. 1GHz is equal to 1000MHz. Almost all processors used in PCs manufactured in the last 15 years have run at speeds exceeding 1GHz. Common speeds for current processors from Intel and AMD exceed 3GHz. The most recent mobile processors used in Android and iOS smartphones and tablets run at speeds exceeding 2GHz. Figure 6-8 compares the clock speeds of typical processors from 1981 to the present.
Exam Preparation Tasks
Review All Key Topics
Review the most important topics in this chapter, noted with the Key Topics icon in the outer margin of the page. Table 6-3 lists these key topics and the page number on which each is found.
Table 6-3 Key Topics for Chapter 6
Key Topic Element |
Description |
Page Number |
Paragraph |
Storage Unit |
|
Capacaties of 4TB drive and a 3TB drive as reported by Windows 10 |
||
Binary KB-PB Capacity in Bytes |
||
Common Data File Types and Typical Sizes |
||
Paragraph |
Throughput Unit |
|
Paragraph |
MHz |
|
Paragraph |
GHz |
Complete the Tables and Lists from Memory
Print a copy of Appendix A, “Memory Tables,” or at least the section from this chapter, and complete the tables and lists from memory. Appendix B, “Memory Tables Answer Key,” includes completed tables and lists to check your work.
Define Key Terms
Define the following key terms from this chapter and check your answers in the glossary:
Practice Questions for Objective 1.5
1. Which of the following is equal to 1024 bytes?
GB
Bit
KB
MB
2. To calculate the number of binary MB in a decimal number, which of the following formulas should be used?
Multiply the value by 1024.
Divide the value by 1,048,576.
Multiply the value by 1,048,576.
Divide the value by 1,000,000.
3. What is the approximate size in binary GB of a DVD+R disc that holds about 4.7 billion bytes?
4.7
4.37
3.48
8.34
4. Choose the largest value from the following list.
1,000,000,000 bytes
950MB
0.78GB
1500KB
5. Choose the largest unit of measure from the following list.
MB
TB
GB
PB
6. Which of the following statements is incorrect?
1024KB = 1MB
1024MB = 1PB
1024GB = 1TB
1TB = 1024MB×1024MB
7. Clock speed measures which of the following?
Data transfer rate
Memory throughput
Device throughput
Processor cycles per second
8. Which of the following is the slowest clock rate?
4770MHz
4GHz
2500MHz
2.7GHz
9. Which of the following is a correct statement about clock speed and CPU performance?
Any processor with a faster clock speed than another performs tasks more quickly.
Internal design has no effect on CPU performance.
A processor’s clock speed is one of the factors determining CPU performance.
A processor’s clock speed is controlled by the real-time clock chip on the motherboard.
10. You are evaluating two laptop computers. One of them has a faster processor than the other. Which of the following is a correct statement about these computers?
The computer with the faster processor will perform all tasks faster.
The processor has no effect on system performance.
The computer with the faster processor has more RAM than the other one.
There is not enough information to determine which computer will perform needed tasks faster.
11. You are creating a digital music (MP3) file from a music track on one of your CDs. Which of the following settings is best if you want to create a high-
quality file?
64Kbps compression.
320Kbps compression.
32-bit compression.
Any setting will work because quality is based on the original track, not the MP3 compression settings.
12. You are examining a computer you want to buy. It needs to have at least two USB ports with a transfer rate of 5Gbps. It has two USB 2.0 ports, two USB 3.0 ports, and one USB 3.1 Gen 2 port. Does this computer meet the requirements? (Choose the best answer.)
Yes, all five ports are fast enough.
No, none of these ports is fast enough.
No, only the USB 3.1 Gen 2 port is fast enough.
Yes, there are three ports that are fast enough.
13. You are comparing two photos—one JPG and one a CR2 RAW file. The pictures are the same resolution. Which of the following is a correct statement about these photos?
The JPG photo uses more disk space than the CR2 file.
The CR2 file uses more disk space than the JPG file.
Both files use the same amount of disk space because they are the same resolution.
The CR2 file was shot with a smartphone.
14. You need to send a 15MB text and image document created in Microsoft Word to a client. Their email service can only accept 10MB files. Which of the following will create a file the other user can review most easily?
Save the file in Rich Text Format and find out if the client can open the file.
Save the file as a series of JPG screen captures.
Save the file as a high-quality PDF.
Edit the file into two or more smaller files and email each separately.
15. Which of the following accurately lists measurements in order from largest to smallest?
Megabyte, kilobyte, petabyte
Petabyte, gigabyte, terabyte
Petabyte, gigabyte, megabyte
Gigabyte, kilobyte, megabyte
16. Which of the following accurately lists connection speeds in order from fastest to slowest?
Fast Ethernet, Gigabit Ethernet, USB 2.0
FireWire 1394a, Fast Ethernet, USB 2.0
USB 3.1 Gen 1, Fast Ethernet, Gigabit Ethernet
USB 3.0, Gigabit Ethernet, FireWire 1394b
17. A processor clock cycle consists of which of the following?
Rising and falling edges of pulse
Space between each pulse
Pulse and rest
Two pulses and space between the pulses
18. Select the correct pairing of binary measurements and size in bytes.
1KB = 1,048,576
1MB = 1,048,576
1GB = 1,000,000.000
1MB = 1,000,000
19. Which of the following is a correct statement about processor type and memory size?
A 32-bit processor can manage up to 32MB of RAM.
A 64-bit processor can manage up to 232 of RAM.
A 32-bit processor can manage up to 4GB of RAM.
A 64-bit processor can manage up to 64GB of RAM.
20. You are using Windows to determine the amount of space left on a hard disk. Which of the following statements is accurate about how Windows displays the capacity?
You must calculate the binary MB or GB capacity manually from the bytes listed.
Windows reports only binary MB or GB capacity; you must calculate the bytes manually.
Windows uses a pie chart to display capacity.
Windows displays binary MB or GB and bytes.
Your Next Steps
If you groove on the idea of faster and faster performance, you may be interested in beefing up your PC building and configuration skills. Check out the CompTIA A+ certification as your next step. You’ll learn how to build, configure, troubleshoot, and manage today’s PCs. The skills you learn will help you deal with anything from office-class laptop PCs to fire-breathing gamer towers.
For more information on CompTIA A+ certification, go to https://certification.comptia.org/certifications.