Risc Business

Although RISC machines have to use many to perform tasks that their rivals could manage with one, they compensate by executing simple very quickly. Several steps are re­quired to perform an in a microprocessor.

First an code is fetched from the memory. Then the microprocessor deciphers this se­quence of 0s and 1s to determine what it is being told to do. Then the results of the operation are stored.

To maintain order within the computer, these operations are performed in strict se­quence, synchronised to the ticking of a central clock. Simpler allow the clock to tick faster.

But me biggest gains come from taking advantage of simplicity to reorganise the flow of work through the chip.

Exercise 8

Read this article from the New Scientist and complete the table below about the devices described in the article. (The first line of the table has been com­pleted for you. If an item of information is not given in the article, put 'not mentioned' in the table.)

How Flash wins when the Chips are Down

...Conner Peripherals of California supplies 2.5 inch disk drives able to store 120 megabytes of data. In contrast, an Intel flash card with up to 20 megabytes of data is about the same size as four credit cards stacked on top of each other: 86 millimetres long, 54 millimetres wide and just 3 millimetres deep.

...If you compare a flash memory card and a typical 2.5 inch drive, flash wins on a number of fronts. Its specified access time, representing the time it takes to retrieve data, is 250 nanoseconds, against 20 milliseconds. Power consump­tion is 250 milliwatts as the memory is ac­cessed and 5 milliwatts when on stand-by; the hard disc consumes 3 watts during access and 500 milliwatts while waiting.

The flash card weighs 28 grams, the hard disc 150 grams. And flush can bear shocks of 50G, compared with 5G for the hard disc....

Hard discs still have their advan­tages. The first is that flash can only be erased a limited number of times, al­though that limit is 100.000 for an Intel flash card. The second, and biggest, is price. A 20-megabyte Intel flash card costs $400 from a short production run of 1.000....

One of the most important attributes of flash memory is its ability to retain data without power, known as 'non-volatility'.

Data can also be erased and re­corded on flash while it is in a computer or other device, although erasing must be done in blocks of kilobytes, rather than bit-by-bit, as is possible with hard discs or other storage media....

	2.5 inch drive	Flash
Capacity	120 megabytes	20 megabytes
Access time
Power consumption during access
Power consumption on standby
Weight
Resistance to shocks
Volatile?
Reprogrammable bit by bit?

Exercise 9

Answer the following questions:

1. What does the article refer to?

2. Just fancy you have to choose between flash memory card and hard disk. What list of pros and cons will you make up to solve the problem?