Memory & Storage: Crash Course Computer Science #19

Introduction to Computer Memory

In this section, Carrie Anne introduces the concept of computer memory and explains the difference between volatile memory and non-volatile storage.

Volatile Memory vs. Non-Volatile Storage

• Volatile memory, such as computer memory, is non-permanent and data is lost when power is disconnected.

• Non-volatile storage, like hard drives, retains data even if power is lost.

Early Forms of Computer Storage

This section explores the early forms of computer storage and their limitations.

Punch Cards

• Punch cards were a popular form of storage in the past due to their low cost and durability.

• However, punch cards were slow and write-once, making them less useful for storing temporary data.

Delay Line Memory

• Delay Line Memory was an early form of computer memory developed by J. Presper Eckert.

• It used a tube filled with liquid (mercury) to store data using pressure waves.

• The propagation delay of these waves allowed for data storage.

Magnetic Core Memory

This section discusses magnetic core memory as a significant advancement in computer storage technology.

Magnetic Core Memory

• Magnetic core memory used small magnetic donuts called cores to store 1's and 0's.

• Each core could be magnetized in one direction or another to represent binary values.

• Cores were arranged into grids with wires for selecting rows and columns.

Conclusion

Computer memory has evolved significantly over time, from punch cards to delay line memory to magnetic core memory. These advancements have led to faster, more reliable, and higher-density storage options.

Magnetic Core Memory

This section discusses the development and features of magnetic core memory as a predominant Random Access Memory technology in the mid-1950s.

Development and Features of Magnetic Core Memory

• Magnetic core memory had roughly 16 thousand bits of storage.

• Unlike delay line memory, any bit could be accessed at any time.

• It became the predominant Random Access Memory technology for two decades starting in the mid-1950s.

• Magnetic core memory was typically woven by hand.

• The cost fell from roughly 1 dollar per bit to around 1 cent per bit by the 1970s.

Storage Challenges and Research

This section highlights the challenges in storage costs and introduces research into storage technologies happening during this time.

Storage Challenges and Research

• Storing data on magnetic core memory was expensive, with an average smartphone photo requiring around 40 million bits.

• The cost of storing a single photo on core memory would be prohibitively high at $400,000.

• Tremendous research into storage technologies was taking place during this time.

• Eckert and Mauchly started their own company and designed UNIVAC, one of the earliest commercially sold computers.

Introduction of Magnetic Tape

This section discusses the introduction of magnetic tape as a new form of computer storage with its features and advantages.

Introduction of Magnetic Tape

• UNIVAC debuted with magnetic tape as a new form of computer storage.

• Magnetic tape was a long, thin, flexible strip of magnetic material stored in reels.

• A tape drive moved the tape forwards or backwards for access.

• Write heads passed current through a wound wire to generate a magnetic field, allowing storage of 1's and 0's.

• Read heads detected the polarity non-destructively.

• UNIVAC used half-inch-wide tape with 8 parallel data tracks, each able to store 128 bits of data per inch.

Magnetic Tape Advantages and Drawbacks

This section explores the advantages and drawbacks of magnetic tape as a storage technology.

Magnetic Tape Advantages and Drawbacks

• Magnetic tape drives were expensive, but the tape itself was cheap and compact.

• Each reel of tape could store roughly 15 million bits, equivalent to almost 2 megabytes.

• Magnetic tape is still used today for archiving data due to its cost-effectiveness and compactness.

• The main drawback of magnetic tape is its access speed since it is inherently sequential.

• Accessing specific data may require traversing hundreds of feet of tape, resulting in slow retrieval times.

Magnetic Drum Memory

This section introduces magnetic drum memory as a popular storage technology in the 1950s and 60s.

Introduction of Magnetic Drum Memory

• Magnetic Drum Memory consisted of a metal cylinder coated in a magnetic material for recording data.

• The drum rotated continuously, with read and write heads positioned along its length.

• Read/write heads waited for the right spot on the drum to rotate underneath them for reading or writing data.

• Drums were rotated thousands of revolutions per minute to minimize delay.

Transition from Magnetic Drums to Hard Disk Drives

This section discusses how magnetic drums led to the development of hard disk drives.

Transition from Magnetic Drums to Hard Disk Drives

• By 1953, units capable of recording 80,000 bits of data were available.

• The manufacture of magnetic drums ceased in the 1970s.

• Magnetic drums directly influenced the development of hard disk drives, which use a different geometric configuration.

• Hard disks consist of stacked disks that are thin and provide a large surface area for data storage.

Introduction of Hard Disk Drives

This section explores the features and advantages of hard disk drives as a storage technology.

Introduction of Hard Disk Drives

• Hard disk drives have a magnetic surface that allows write and read heads to store and retrieve 1's and 0's.

• Disks are thin and can be stacked together, providing ample surface area for data storage.

• IBM introduced the world's first computer with a disk drive, the RAMAC 305, which contained fifty 24-inch diameter disks.

• The RAMAC 305 had a total storage capacity of roughly 5 megabytes.

Accessing Data on Hard Disk Drives

This section discusses how data is accessed on hard disk drives and the associated seek time.

Accessing Data on Hard Disk Drives

• Read/write heads travel up or down the stack of disks to access any block of data.

• The heads wait for the right section to come around as the disks spin.

• The average seek time on the RAMAC 305 was around 6/10ths of a second.

• To improve memory speed, the RAMAC 305 also incorporated drum memory and magnetic core memory.

Memory Hierarchy

This section explains the concept of memory hierarchy and its role in balancing cost and speed.

Memory Hierarchy

• Memory hierarchy involves having different levels of memory with varying speeds and costs.

• A little bit of fast memory, such as magnetic core memory, is expensive but provides high-speed access.

• Medium-speed memory, like drum memory, is less expensive.

• Slowish memory, such as hard disk drives, is cheap but slower in terms of access speed.

• This mixed approach balances cost and speed.

Advancements in Hard Disk Drives

This section highlights the rapid improvements in hard disk drives and their increased storage capacity.

Advancements in Hard Disk Drives

• By the 1970s, hard disk drives became commonplace and could hold 1 terabyte of data today.

• Modern hard drives can store roughly 200,000 five-megabyte photos.

• The cost per bit has significantly decreased to 0.0000000005 cents per bit.

• Average seek time on modern hard drives is under 1/100th of a second.

Floppy Disks and Optical Storage

This section introduces floppy disks and optical storage as additional storage technologies.

Floppy Disks and Optical Storage

• Floppy disks were similar to hard disks but used a floppy magnetic medium.

• They were commonly used for portable storage from the mid-1970s to the mid-90s.

• Higher density floppy disks like Zip Disks gained popularity in the mid-1990s but fell out of favor later on.

• Optical storage was introduced in 1972 with the "laser disc," which was a 12-inch optical disc.

New Section

This section discusses the evolution of storage technologies from optical sensors to solid-state drives, and the use of integrated circuits in RAM.

Evolution of Storage Technologies

• Light is reflected differently on surfaces, captured by optical sensors, and decoded into 1's and 0's.

• Solid-state technologies like hard drives and USB sticks are replacing traditional storage devices with moving parts.

• Solid State Drives (SSDs) have no moving parts, resulting in faster access times compared to hard disk drives.

• Memory and storage technologies have followed an exponential trend, becoming more affordable over time.

The timestamps provided above correspond to the approximate starting points for each bullet point.