RAM ROM • Stand for Random-Access Memory • Stand for ..., Summaries of Computer Applications

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• The differences between RAM and ROM :-

RAM ROM  Stand for Random-Access Memory

 Stand for Read Only Memory

 Read / Write Memory  Read Only Memory

 Sending data (writing) to RAM memory address is called destructive write because the new data erases whatever was there before.

 Sending data to ROM memory address is in effective because the contents of ROM cannot changed (write not allowed) because this memory for read only.

 Form of primary storage for holding temporary data and instruction

 Form of primary storage for holding permanent data and instruction  Volatile :program and data are erased when the power is off

 Permanent :program and data are intact even power is off  Type of RAM is  Static RAM  Dynamic RAM

 Type of ROM is  PROM  EPROM  EAPROM

3-Cache Memory: many modern computer applications (Microsoft office 98, for example) are very complex and have huge numbers of instructions it takes considerable RAM capacity (usually a minimum 16MB) to store the entire instruction set. Or you may be using an application that exceeds your RAM. In that case, your computer has to go into secondary storage to retrieve the instruction. To alleviate this problem, software is often written in smaller blocks of instruction. As need, these blocks can be brought from secondary storage into RAM; this is still slow however, cache memory is the place closer to the CPU where the computer can temporarily store those blocks used most often. Those used less often remain in RAM until they are transferred to cache; those used infrequently stay stored in secondary storage. Cache memory is faster than RAM. Because, the instructions travel a shorter distance to the CPU.

4- Flash memory: is one such device. This memory can be accessed like RAM (read and written), but is non-volatile i.e. it is a form of permanent storage. At the time of writing flash memory is available in the 512Mb to 1GB range. One disadvantage of current NVRAMs is that they cannot be written

to, as quickly as ordinary RAM. However, they are much faster to access than disk storage systems and they consume less power, so that in small portable computer

systems they offer an alternative low-powered option to disk storage. However, NVRAMs are more expensive than disk storage devices.

5 - Virtual Memory: If your computer lacks the random access memory (RAM) needed to run a program or operation, Windows uses virtual memory to compensate. Virtual memory combines your computer’s RAM with temporary space on your hard disk. When RAM runs low, virtual memory moves data from RAM to a space called a paging file. Moving data to and from the paging file frees up RAM to complete its work. The more RAM your computer has, the faster your programs will generally run. If a lack of RAM is slowing your computer, you might be tempted to increase virtual memory to compensate. However, your computer can read data from RAM much more quickly than from a hard disk, so adding RAM is a better solution.

نظاملتشغيل برنامج أو عملية، يستخدمكافية(RAM)عشوائيإلى ذاكرة وصولالحاسبة في حالة افتقار جمعبالافتراضبةرةقوم الذاكتالافتراضبةذاكرةالللتعويض. لمعرفة حجمافتراضبةذاكرةWindowsتشغيل ال ذاكرةاداءانخفاضعندمع مساحة مؤقتة على القرص الثابت.بالحاسبةلخاصةا)RAM( ذاكرة الوصول العشوائي تنقل الذاكرة الظاهرية البيانات من ذاكرة الوصول العشوائيإلى مساحة تُعرف باسم)RAM( الوصول العشوائي مساحة علىيحرروإليه paging file ن ملف ترحيل الصفحاتنقل البيانات م. paging file ملف ترحيل الصفحات على الحاسبة)RAM(حجم الRAMعدد الانككلما.امكن من إكمال عملهتتحتىالوصول العشوائي ذاكرة يتسبب في)صغيرRAMال(حجم)(اي عددحالةوعكس هذه ال.اسرعتشغيل البرامج بشكل عامكونيسكلما كبير قراءةمنتمكنتحاسبةالالا ان.للتعويضالافتراضيةتبدا في زيادة الذاكرةه الجالةفي هذ،الحاسبة بطىء الىRAMضافةاانلذلك، البيانات من ذاكرة الوصول العشوائي بسرعة اكبر من قراءتها من القرص الثابت .حلافضليعتبر الحاسبة

-Bios : Short for ( B asic I nput / O utput S ystem), Bios is a chip located on all

computer motherboard that contains instructions and setup for how your

system should boot and how it operates. To the right is a picture of what a

BIOS chip may look like in your computer. The BIOS includes instructions

on how load basic computer hardware and includes a test referred to as a

POST ( P ower O n S elf T est) that helps verify the computer meets

requirements to boot up properly, if the computer does not pass the POST ,

3- Data is stored in tracks; there are 7 or 9 tracks (depending on the tape unit) which run the length of the tape. The data is recorded so that one character is recorded across the 7 or 9 tracks. 4- The density of recording can vary between 2 5- It is serial access device.

6- The tape is reusable i.e. it can be overwritten 7- The same tape can be used for input and output. The tape can be writing protected.

B-Features of magnetic disks (hard disks)

1. Disks are randomly accessed.
2. Disks are of size and shape similar to a long-playing record
3. The surfaces of each disk are of magnetic able material.
4. Each disk surface is divided into a number of concentric tracks (typically 200).
5. Disks are placed on pack and each pack may have 6 or 11 disks and is used as a single unit.
6. The latest models of disk packs can store many hundreds of megabytes of data (i.e. hundreds of millions of characters).

C-Features of floppy disks 1- A pliable disk permanently sealed with a rigid, protective plastic envelope

2- They have random access facility.

3- Data are stored in concentric tracks

4- The floppy disks sizes are 8, 5 1/4, 3 1/2 inch.

5- Storing capacity of 3 1/2 inch disks is 1.44 megabytes i.e. one million four hundred thousand characters.

Floppy Disk (1.44MB)

D-Features of optical disks 1- This is a random access device.

2- Data is written into the disk by burning a permanent pattern into the surface of the disk by means of high precision laser beam.

3- Data is read by using the laser at lower intensity and detecting the pattern reflected from its beam by the surface of the disk there are many types of optical disks: a- Compact disk read-only memory (CD-ROM) storing devices feature high capacity, low cost. It has become popular for recorded music as well as information (such as books) a variant is the digital video disk (DVD), used for movies. b- Write once, read many (WORM) disk can be written. c- Rewritable CD is a less common technology that allows the disk to be written upon and written up to 1.000 times.

Hard Disk Performance: Several basic parameters determine the performance of a given hard disk drive. A seek operation is the movement of the read/write head to the desired track.

1- Seek Time: A seeks time is the movement of the read\write head to the desired track. The seek time is the average time for this operation to be performed. Typically, hard disk drives have an average seek time of several milliseconds, depending on the particular drive.

2- Latency Time: The latency period is the time takes for the desired sector to spin under the head once the head is positioned over the desired track. Latency time depend on the constant rotational speed of the disk.

• The sums of average seek time and the average latency time is the access

time for the disk drive.