Lecture 06: Computers Memory

Summary

This lecture covers the fundamentals of computer memory, including primary and secondary memory. It explains the differences between **RAM** (Random Access Memory) and **ROM** (Read-Only Memory), their types, and characteristics. Key differences in **static RAM** (SRAM) and **dynamic RAM** (DRAM) are highlighted, with a focus on DDR technologies (DDR1, DDR2, DDR3, DDR4). The lecture also explores various secondary storage devices such as **hard disks**, **SSDs**, **floppy disks**, **CDs/DVDs**, and **USB drives**, discussing their performance, access times, and storage capacities. This comprehensive overview helps students understand the essential components of computer memory systems.

Takeaways

• 😀 Primary memory is directly accessible by the CPU, while secondary memory is not. Primary memory is faster but has a smaller capacity compared to secondary memory.
• 😀 RAM (Random Access Memory) is volatile and can be read from and written to, while ROM (Read Only Memory) is non-volatile and data is not easily modified.
• 😀 RAM is classified into static RAM (SRAM) and dynamic RAM (DRAM), with SRAM being faster and more reliable but more expensive than DRAM.
• 😀 DRAM is further divided into types such as SDRAM, ESDRAM, and DDR, with DDR offering the highest data transfer speeds, particularly DDR4.
• 😀 Secondary memory includes storage devices like hard disks, SSDs, CDs, DVDs, USB flash drives, and memory cards. These are used for long-term data storage.
• 😀 Hard disks store data on magnetic platters, with components like tracks, sectors, and cylinders. The performance of a hard disk depends on seek time, rotational time, and transfer time.
• 😀 SSDs (Solid State Drives) are faster, more reliable, and consume less power than hard disks. They are used to enhance system speed and allow faster data transfer.
• 😀 Floppy disks, which were widely used from the 1970s to 2000, have very limited storage capacity and are slower compared to modern storage devices.
• 😀 CDs (Compact Discs) and DVDs (Digital Versatile Discs) are optical storage media, with DVDs offering larger storage capacity and better quality for video and audio data than CDs.
• 😀 Memory cards, such as those used in smartphones and cameras, are portable, non-volatile storage devices that are available in a variety of sizes and can store personal files like documents and photos.

Q & A

What is the difference between primary and secondary memory?

Primary memory is directly accessible by the CPU, stores data currently in use, is faster, and has smaller capacity. Secondary memory, on the other hand, cannot be accessed directly by the CPU, stores data not actively in use, is slower, and has larger storage capacity.

What is the difference between RAM and ROM?

RAM (Random Access Memory) is volatile, meaning it loses data when the system is powered off, and allows both reading and writing. ROM (Read-Only Memory) is non-volatile, meaning it retains data even when powered off, and typically allows only reading, with limited writing capabilities.

What are the types of ROM and their characteristics?

ROM comes in several forms: PROM (Programmable Read-Only Memory) is programmed once and cannot be modified; EPROM (Erasable Programmable Read-Only Memory) can be erased with ultraviolet light and reprogrammed; and EEPROM (Electrically Erasable Programmable Read-Only Memory) can be erased and reprogrammed electrically, providing the highest flexibility.

What is the difference between static RAM (SRAM) and dynamic RAM (DRAM)?

SRAM is faster and does not need to be refreshed, but it requires more transistors and is more expensive. DRAM, which uses capacitors to store data, requires constant refreshing, is cheaper, and can store more data in the same physical space.

What is DDR RAM and how is it different from its predecessors?

DDR (Double Data Rate) RAM allows data transfer on both the rising and falling edges of the clock signal, doubling its data transfer rate. DDR2, DDR3, and DDR4 represent advancements, with DDR4 offering the fastest speed, increased capacity, and improved efficiency compared to earlier versions.

What are secondary memory devices, and how do they differ from primary memory?

Secondary memory devices include hard disks, SSDs, floppy disks, CDs, DVDs, and USB drives. Unlike primary memory, secondary memory is non-volatile, has larger capacity, and is cheaper, but it is slower and not directly accessible by the CPU.

How does a hard disk store data?

A hard disk stores data on magnetic platters that rotate, with read/write heads that move over the surface. Data is written in tracks (concentric circles) divided into sectors. The performance of the hard disk depends on its seek time, rotational delay, and transfer time.

What are the advantages of SSDs over traditional hard disks?

SSDs are faster, more reliable, and consume less power than hard disks. They also have no moving parts, making them more durable and silent. SSDs offer better speed for booting up systems and data transfer compared to traditional hard drives.

What is the main difference between CDs and DVDs?

The main difference is capacity. CDs store around 700 MB of data, primarily used for audio, whereas DVDs store much more, ranging from 4.7 GB (single layer) to 8.5 GB (dual layer), and are used for storing video and higher quality data.

What is magnetic tape, and how does it differ from other storage media?

Magnetic tape is a sequential access storage medium, meaning it requires the tape to be physically moved to find specific data. Unlike RAM, which is random access, magnetic tape is slower and was commonly used for backups and archival purposes in the past.