Explain like I'm five · Law/Policy

What is IS Hardware Sizing?

The IS hardware sizing guideline, told as a story about the student council calculating festival food quantities with a formula ahead of time.

how many tteokbokki servings do we make?last year it was 300 servings…guessing the amount of food means too little or too much

Nobody knows how many festival servings to make.Guessing the amount of food means either too little or too much.

made way too much and had to toss itforgot more students transferred inbudget and headcount change each year, so an amount guessed without a formula comes out wrong

Just guessing the food amount high, or copying last year's, gets it wrong.Budget and headcount change each year, so an amount guessed without a formula comes out wrong.

a sizing guideline = a formula sheet that works out the amount needed from expected headcount and usageSIZING FORMULAexpected headcountpeak concurrent useadd a safety marginfactor next year's growththe amount is decided by numbers in advance, not by gut feel

The sizing guideline is a formula sheet that works out, in advance, how much server and storage capacity is needed.The amount is decided by numbers in advance, not by gut feel.

Gather past datastart from past usage
Look at the busiest momentsized for the peak, not the average
Add a safety marginadds extra on top of the exact need
Re-measure periodicallyit's never a one-time job
EXAMPLE: A 1,200-STUDENT FESTIVALexpected headcount: 1,200peak participation × 60% = 720safety margin × 1.3 ≈ 936 servingsnext-year growth × 1.1 ≈ prepare 1,030 servingsthe same inputs give anyone the same answer

Applied to a 1,200-student festival, the formula gives about 1,030 servings.The same inputs give anyone the same answer.

1,030 servings readya neighboring school showed up too!the formula is a starting point — actual usage still has to be watched and re-measured

Even after preparing by the formula, the crowd can suddenly change.The formula is a starting point — actual usage still has to be watched and re-measured.

In one breath

Hardware sizing = a formula sheet that multiplies expected headcount and usage by peak load, safety margin, and growth rate, calculated in advance.

The IS hardware sizing guideline is a TTA (Korea's ICT standards body) standard, TTAK.KO-10.0292, used in public-sector IT projects, with server performance expressed in units like tpmC and OPS. It calculates server and storage capacity with formulas based on expected users, transaction counts, and data volume. It adds a correction for peak-hour load, plus a margin for unexpected growth in work.

When grown-ups say it

Capacity Sizing
Measuring the needed amount in advance with a formula. Leaves a numeric basis, not just a guess.
TPS (Transactions Per Second)
Units of work (like orders) handled per second. A common throughput unit; this guideline uses units like tpmC and OPS instead.
Peak Load
The amount at the busiest moment. Sizing by average falls short at the busiest moment.
Safety Margin
The extra percentage added instead of cutting it exact. Lets the system hold up even if demand suddenly rises.
Growth Projection
Building in next year's expected increase. Because hardware, once bought, has to last several years.
Availability
How much a service must keep running without stopping. Another field covers this alongside sizing. → the ticket that guarantees the show
Capacity Planning
Planning how much more will be needed ahead of time. A similar plan exists in another field too. → planning more seats ahead of time
Benchmark Test
Testing how much load the hardware can actually handle. Not trusting the formula's result alone — testing it for real.
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