PC Hardware

# Tutorial 7

1. What is hexadecimal shorthand used for?

Hexadecimal shorthand (hex, for short) is a numbering system used by designers and programmers to simplify the representation of numbers and notations. Known as "base-16 mathematics," it is a complete numbering system based on 16 instead of 10. Just as in the base-10 system, you can add, subtract, or do trigonometry with hex.

2. Define the following terms: conventional memory, expanded memory, extended memory, HMA, shadow RAM.

Conventional memory is the first 640 KB of memory in a computer. The first 1 MB of memory was divided into two sections: 384 KB of RAM (designated upper memory) for running the computer (BIOS, video RAM, and ROM), and 640 KB for applications (designated).

Expanded memory is memory that conforms to the EMS specification, developed by Lotus, Intel, and Microsoft. It requires a special device driver. EMS is accessed through 64-KB blocks of the upper memory.

Extended memory is any memory beyond the first 1 MB.

HMA is the first 64 KB of extended memory on machines with 80286 or higher processors.

Shadow RAM rewrites (or shadows) the contents of the ROM BIOS and/or video BIOS into extended RAM memory (between the 640-KB boundary and 1 MB). This allows systems to operate faster when application software calls for any BIOS routines.

3. Describe the difference between ROM and RAM.

ROM is read-only memory and cannot be changed. It is usually used for BIOS or other data that cannot be lost if the power is off.

RAM is random access memory and is constantly changing. It is used as the main working memory for a computer. RAM memory is lost if the power is turned off.

4. How many 30-pin SIMM boards are required for one bank of memory on a computer with a 486 processor?

Because a 486 computer has a 32-bit external data bus, it requires four 30-pin SIMMs per bank. Remember, a 30-pin SIMM is only one byte (8-bits) wide; therefore, you need to divide the width of the bus by the width of the SIMM-that is, 32 (the width of data bus) divided by 8 (the number of bits per SIMM module).

5. What is the difference between "write-through" and "write-back" cache?

Some caches immediately send all data directly to RAM, even if it means hitting a wait state. This is called write-through cache. Some caches store the data for a time and send it to RAM later. This is called a write-back cache.

6. What is DRAM?

DRAM (dynamic random access memory) is volatile memory that works only when the computer has power. This is the "scratch pad" that the CPU uses to manipulate data.

7. Define access speed.

The time required to complete a memory read or to write actions is known as the access speed of the memory chip. This time is usually very small and is measured in nanoseconds (one-billionth of a second-abbreviated as ns). The faster the chip, the smaller the access-speed number.

8. Describe the major difference between SIPPs and SIMMs.

A SIPP (single inline pin package) is a printed circuit board with individual DRAM chips mounted on it. SIMMs (single inline memory modules) are the new generation of memory chips. They are similar to SIPPs, with one exception-SIMMs have no pins, as such. 30-pin SIMMs have 30 contacts along the edge.

9. Define cache memory.

To cache means to set something aside, or to store nearby, for anticipated use. Mass storage (disk drives) is much slower than RAM, and RAM is much slower than the CPU. Caching increases the speed of the system by creating special storage areas in high-speed memory.

10. One of the differences between DRAM and SRAM is that SRAM does not have to be refreshed. What does this mean, and how does it affect the cost of each type of chip?

Refreshing means that the information must be updated constantly or it will be lost. SRAM does not require that extra step that can slow things down (nothing can access the memory during a refresh). Because SRAM is faster, the circuitry required is more expensive.

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