Computer and Memory

Topics: CPU cache, Computer, Virtual memory Pages: 5 (1497 words) Published: March 18, 2014

Operating Systems

Assignment: HW1

Done by: Ahmed Saad Hamed

ID: 1013620

CSC308 (Operating Systems
Spring 2013/2014
Dr. Ashraf Khalil
Due date: Saturday, 15th, 2014 (by Midnight)

1. Consider a 32-bit microprocessor, with a 16-bit external data bus, driven by an 8-MHz input clock. Assume that this microprocessor has a bus cycle whose minimum duration equals four input clock cycles. What is the maximum data transfer rate across the bus that this microprocessor can sustain in bytes/s? Since minimum bus cycle duration = 4 clock cycles and bus clock = 8 MHz Then, maximum bus cycle rate = 8 M / 4 = 2 M/s Data transferred per bus cycle = 16 bit = 2 bytes Data transfer rate per second = bus cycle rate * data per bus cycle = 2 M * 2 = 4 Mbytes/sec.

2. A computer has a cache, main memory, and a disk used for virtual memory. If a referenced word is in the cache, 20 ns are required to access it. If it is in main memory but not in the cache, 60 ns are needed to load it into the cache (this includes the time to originally check the cache), and then the reference is started again. If the word is not in main memory, 12 ms are required to fetch the word from disk, followed by 60 ns to copy it to the cache, and then the reference is started again. The cache-hit ratio is 0.9 and the main-memory hit ratio is 0.6. What is the average time in ns (Nano second) required to access a referenced word on this system? 90% (0.9) is the time it is in cache.

0.10% * 60% (0.06) is the time it is not in cache but is in memory. 4% (0.04) (obtained from 1-90% - 6%) of the time it is neither in cache or memory

0.9 (20ns) +0 .06 (60 ns + 20ns) + .04 (12ms + 60ns +20ns)
18ns + 4.8ns + .48ms (I've dropped the rest because it is minimal compare to the access to disk) = 480 microseconds

3. A user program begins at t=0. At t =10, a printer interrupt occurs and at t=15, a communications interrupt occurs and at t=20, a disk interrupt occurs. Given the service times of 20, 30, and 10 for printer interrupt, communication interrupt, and disk interrupt respectively, and the desk interrupt has the highest priory followed by printer and then communication interrupt. Which one of the following statements give the correct finish times for the printer interrupt.

4. What does PC register stands for? What value does it hold?

It keeps track of the next memory address of the instruction that is to be executed once the execution of the current instruction is completed. In other words, it holds the address of the memory location of the next instruction when the current instruction is executed by the microprocessor. 

5. What is a memory word? And what does it contain?
Internal storage areas in the computer. The term memory identifies data storage that comes in the form of chips, and the word storage is used for memory that exists on tapes or disks. Moreover, the term memory is usually used as shorthand for physical memory, which refers to the actual chips capable of holding data. Some computers also use virtual memory, which expands physical memory onto a hard disk. Every computer comes with a certain amount of physical memory, usually referred to as main memory or RAM. You can think of main memory as an array of boxes, each of which can hold a single byte of information. A computer that has 1 megabyte of memory, therefore, can hold about 1 million bytes (or characters) of information. There are several different types of memory:

RAM (random-access memory): This is the same as main memory. When used by itself, the term RAM refers to read and write memory; that is, you can both write data into RAM and read data from RAM. This is in contrast to ROM, which permits you only to read data. Most RAM is volatile, which means that it requires a steady flow of electricity to maintain its contents. As soon as the power is turned off, whatever data was in RAM is lost. ROM (read-only...
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